The present invention relates to a new and distinct cultivar of peach rootstock (Prunus persica) that has been denominated as ‘HBOK 27’, and more particularly to a peach rootstock that is graft compatible with peach and nectarine scion cultivars, confers moderate vigor control on compound trees [approximately 30-40% reduction based on trunk cross sectional area (TCA) and tree height], produces fewer root suckers than the standard rootstock ‘Nemaguard’, and has moderate resistance to the root knot nematode Meloidogyne incognita (race 1) isolate ‘Beltran’. Moreover, peach trees grown on the ‘HBOK 27’ rootstock are productive and require less pruning than trees grown on the standard rootstock ‘Nemaguard’.
It is recognized that vigor control of compound trees on a standard rootstock, such as ‘Nemaguard’, is difficult to achieve and to do so requires extensive pruning both in mid summer and the dormant season. It is also recognized that root suckers produced on standard rootstock are required to be removed manually resulting in costs to the grower. The ‘HBOK 27’ peach rootstock has moderate vigor control that produces smaller trees, requires less pruning, and produces much fewer root suckers than the standard rootstock ‘Nemaguard’. These characteristics result in cost savings for the grower.
The research during which the original tree was first selected as a potential clonal rootstock was conducted at Davis, Calif. In Year 1, the hybrid ‘P248-139’ was created by crossing ‘Harrow Blood’ (HB) with ‘Okinawa’ (OK) at Fresno Calif. ‘Harrow Blood’ was used as the female parent and ‘Okinawa’ was used as the male parent in the cross. Seeds resulting from the open pollination of a single F1 plant from hybrid ‘P248-139’ were used to generate an experimental population (referred to as ‘OP-F2 population’) in February of Year 5. Fifty seven ‘OP-F2’ seedlings were budded with ‘O'Henry’ (referred to as ‘O'Henry population’) and concurrently each of these seedlings was budded onto ‘Nemared’ rootstock (referred to as ‘OP-F2 population’). Of the 57 budded ‘OP-F2’ seedlings, 49 were successful bud unions for the seedlings as both a scion and rootstock. However, for seven of the pairs, either the scion union or rootstock union was unsuccessful and had to be re-budded.
The seedling ‘94-94-27’ (‘HBOK 27’) was one of the bud unions that was re-budded in September of Year 7. After the re-budding, there were no obvious defects in the bud unions, indicating the compatibility of scions and rootstocks. Compound trees of ‘O'Henry’ scion budded onto each seedling of the ‘OP-F2’ segregating population as a rootstock were evaluated for trunk cross-sectional area (TCA), tree height, crop yield, cropping efficiency, fruit weight, and number of suckers. Plants of the ‘94-94-27’ seedling were selected for further study of rootstock potential based on field observations of compound plants grown at Davis, Calif. in Year 11 and Year 12. The primary criteria used for choosing seedlings having potential for size control as a rootstock were tree size and TCA. However, other growth and fruit characteristics were also noted. Leafy cuttings collected from the original trees were propagated asexually (rooted), budded with ‘O'Henry’ peach scion and planted in a replicated field trial under semi-commercial conditions at Parlier, Calif. in Year 15. As a result of that trial ‘HBOK 27’ was identified as having commercial rootstock potential.
In a separate set of experiments, 7 year-old compound trees of ‘HBOK 27’, ‘HBOK 10’, ‘HBOK 32’, ‘HBOK 50’, and ‘Nemaguard’ were studied to determine the mechanism of size control (Tombesi et al., 2011). Compared to those rootstocks and the standard, ‘Nemaguard’, the new peach rootstock ‘HBOK 27’ was the most size controlling. Root knot nematode resistance response of each ‘OP-F2’ seedling in the segregating population was determined using a greenhouse pot test for resistance to M. incognita. The test was completed in Year 13, and it was determined that ‘HBOK 27’ had a moderate resistance rating that was slightly less than the resistant check rootstock ‘Nemaguard’.
The new ‘HBOK 27’ peach rootstock of the present invention has been asexually reproduced by leaf cuttings at Davis, Calif. The distinctive characteristics of the new peach rootstock have been found to be stable and are transmitted to the new rootstocks when asexually propagated.